This invention relates to a method of manufacturing a rotator body made of aluminum used as a rotor of a motor by cutting operation, and a method of manufacturing a motor incorporating the rotor.
Hitherto, rotator bodies made of aluminum have been widely adopted as rotors of motors used with hard disk drives (HDDs) and polygon mirror drives. For example, a rotation hub 1 made of aluminum, a rotor, used with a motor for a hard disk drive shown in FIG. 2 comprises a bearing (not shown) attached to an inner peripheral face 1a of the rotation hub 1 for forming a rotor drive section of the motor. A recording medium disk of a rotated body (not shown) is placed on an outer peripheral face 1c of the rotation hub 1.
To manufacture a rotor made of aluminum for a motor typified by the rotation hub 1, first a blank provided integrally with a yoke is manufactured by aluminum die casting, etc., (step ST1) and is cut to predetermined dimensions for forming a rotator body made of aluminum used as a motor rotor (step ST2), for example, as shown in FIG. 3. Cutting oil is used for the cutting; the remaining cutting oil on the rotator body after the cutting step is removed at the following cleaning step ST3.
To remove the cutting oil at the cleaning step, a solvent is used because it is hard to remove the oil component in pure water. Generally, for example, a chlorine-family solvent of trichloroethylene, methylene chloride. tetrachloroethylene, etc., is adopted as the solvent. Since the chlorine-family solvent is dried extremely rapidly, treatment can be executed at low costs by a simple unit.
To built the rotation hub thus cleaned in the solvent in a motor, the rotation hub is transported to the following parts assembling step. The parts assembling step is not necessarily executed at the same location or area as the rotator body cutting step, and is often executed in a different area. The rotation hub after cleaned in the solvent is often transported to a different area, for example, a remote site and thus is packed in vacuum at step ST4 to prevent corrosion, etc., and is transported at step ST5. In the parts assembling step after the rotation hub is transported, first a visual inspection is executed at step ST6, then the rotation hub is built in a motor, namely, parts assembling is performed at step ST7. That is, as shown in FIG. 2, an annular magnet 3 is attached via a back yoke 2 to the inner peripheral face of an annular yoke part 1b integrated in the opening margin on the bottom of the rotation hub 1 in FIG. 2. In the state, again as shown in FIG. 3, the rotation hub 1 is cleaned in pure water with a neutral detergent at step ST8, then is built in a stator of the motor as finish assembling of a finished product at step ST9. Last, an inspection is executed at step ST10.
However, in the manufacturing method of the rotator body made of aluminum in the related art, it is difficult to completely clean and remove the chlorine-family solvent used for cleaning the cutting oil in the solvent described above, thus the remaining chlorine-family solvent reacts with the aluminum material to cause corrosion and produce aluminum chloride (AICI3) as a white spot-like corrosion portion on the aluminum surface at the assembling time or at the actual use time. The corrosion portion of aluminum chloride (AICI3) has a possibility that it will peel off the surface of the rotor and fly. For example, if the rotor made of aluminum is used with a hard disk drive motor, the corrosion portion may peel off the surface of the rotor and lead to the surface of a recording medium disk, causing a problem of head crash, etc., to occur.
From such a problem, it is also possible to use a hydrocarbon-family solvent without using a chlorine-family solvent to clean cutting oil in a solvent. In this case, however, the solvent drying speed becomes extremely low, thus the solvent drying step involves large facilities; it is hard to adopt a hydrocarbon-family solvent from the viewpoint of the manufacturing costs.
It is therefore an object of the invention to provide a manufacturing method of a rotator body made of aluminum wherein cutting oil can be well removed from the rotator body in a short time and a manufacturing method of a motor incorporating the rotor.
In order to achieve the above object, after a solvent cleaning step of a rotator body using a chlorine-family solvent, an alkaline degreasing step using an alkaline degreasing agent is executed for cleaning the rotator body, and the rotator body after undergoing the solvent cleaning step is simply immersed in a treatment tank storing alkaline degreasing agent, whereby the chlorine-family solvent remaining on the rotator body or aluminum chloride produced by the chlorine-family solvent reacting with aluminum material reacts with the alkaline degreasing agent is removed easily and well.